In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a vascular passageway and which are subsequently expandable into contact with the walls of the passageway. These devices include, among others, blood clot filters which expand and are held in position by engagement with the inner wall of a vein, such as the vena cava. Vena cava filters are known in the art as described, for example, in U.S. Pat. Nos. 4,425,908, 5,669,933 and 5,836,968 and European Patent Office publication 0 188 927 A2, which are hereby incorporated by reference in their entireties. These vena cava filters are generally designed to remain in place permanently. Such filters include structure to anchor the filter within the vena cava, such as elongate diverging anchor members with hooked ends that penetrate the vessel wall and positively prevent longitudinal migration in either direction within the vessel. The hooks on filters of this type are rigid and will not bend, and within two to six weeks after a filter of this type has been implanted, the endothelium layer grows over the diverging anchor members and positively locks the hooks in place. Any attempt to remove the filter thereafter risks injury to or rupture of the vena cava. Nevertheless, a number of vena cava filters have been fitted with a hook on the hub that can be snared and used to pull the filter into a catheter for removal, an example of which is disclosed in U.S. Pat. No. 5,836,968, which is hereby incorporated by reference in its entirety.
Most existing filters, including filters currently present in patients, are not configured to be removable or fitted with an extraction hook and their configurations render them difficult or potentially dangerous to remove. In addition to the challenge of disengaging the filter members from the endothelium without rupturing the blood vessel, there is the difficulty of locating and acquiring the filter so that it can be withdrawn from the vessel into an intravenal catheter. Accordingly, there is a need for an apparatus that can safely locate, capture and remove a blood filter from a patient without the need for major surgery.